Nicole, 23, hinted at the split on her Twitter around 8pm Dec. 18 with a wistful entry: "'Sometimes when you truly love someone you have to let them go.....' I never really understood that quote until now."

The night before, however, the former Playboy Playmate was feeling festive. A source tells UsMagazine.com that Nicole "celebrated her breakup" with a 12-strong crew of girlfriends at Hyde Lounge in West Hollywood.

Her single-lady party continued on Dec. 19, when the model hosted a shindig at Chicago's Manor nightclub. An insider at Manor tells UsMagazine.com that Nicole was "telling everyone" about her Dec. 17 breakup. "She made it sound like it was his doing, saying, 'He said he needs time to 'find himself. I don't have time for that.'" Her ex Jenner, she told friends, has "gone to Australia" for some soul-searching.

Jenner himself tweeted about starting "a new life" Down Under on Dec. 19. "So I decided to stay in Australia BY MYSELF!!! Hahaha this is Crazy.. Might just stay here and start a new life."

Despite the sad news, Nicole wasn't in a gloomy mood at Manor, the source says. "She didn't seem bothered by the recent breakup at all. She spent the entire night downing Jager shots and flirting with all of the guys."

Indeed, her tweets from that night bear that out. "Rocking out at Manor" she wrote a 1:33am on Dec. 20. "Jager time!"

By 11:30am, she was feeling the effects of all those Jagermeister shots: "8 hours of sleep, too much jager= not good."

On the just-concluded fifth season of "The Hills," Nicole and Jenner argued about his flirty relationship with aggressive ex-girlfriend Kristin Cavallari. "Everything was totally fine before you came here, so you need to go back to wherever it is that you came from," Nicole sniped at Cavallari in one heated exchange on the show.

Awkward alert: all three are signed on to shoot the sixth season of "The Hills" early next year.